A leading cause of partial or total blindness in humans, especially the elderly, is cataracts--which is defined as a condition of opacity of the eye's naturally transparent lens through which light entering the eye is focused to the fovis centralis of the retina to form images of viewed objects. As cataracts progress, opacity of the afflicted lens increases and less and less light is transmitted through the lens to the retina, thereby causing an individual's sight to deteriorate, in worst case, to complete blindness.
Because opacity of a natural ocular lens cannot currently--and probably not in the foreseeable future--be reversed or eliminated, the only "cure", previously and still available, for severe cataracts is surgical removal of the afflicted natural lens in its entirety.
After removal of the natural lens, the patient's vision, until relatively recently, was restored to a greater or lesser extent by fitting him or her with spectacles which provided the light focusing previously provided by the natural lens before the formation of cataracts. Spectacles having very thick, heavy and unattractive "coke-bottle" lenses were typically needed to restore reasonably normal vision to the patient.
As a more satisfactory alternative to the thick spectacles used after natural lens removal, artificial lenses, called intraocular lenses, have been developed over the last few decades and are now commonly used as in situ replacements for removed natural lenses. This superior means of restoring a patient's vision after cataract surgery arose after the serendipitous discovery by Dr. Peter Ridley during World War II that embedded fragments of perspex (PLEXIGLAS.RTM.) from shattered wind screens of fighter aircraft were tolerated for long periods of time in the eyes of British pilots. This discovery by Dr. Ridley of the biocompatibility of perspex, a polymethylmethacrylate (PMMA) plastic, gave rise to the surgical practice of implanting artificial lenses inside the eye.
Until the early 1980's, natural lenses, which are typically about 8 (eight) mm in diameter, were surgically removed in one piece from the patient's eyes through ocular incisions that were about the same length as the diameter of the removed lenses. Replacement IOLs are typically implanted in the same surgical procedure in which the natural lens had been removed through the same ocular incision made to remove the natural lens. Consequently, rigid IOLS, typically constructed from PMMA, and having about a six mm optic, could be readily implanted, for example, by the use of forceps, without enlarging the original lens removal incision.
In the late 1970's, techniques and equipment were developed by which a natural lens could be ultrasonically broken-up and suctioned out of the lens capsular bag which surrounds it with an irrigation solution and cannula. This improvement allowed an incision of only about 3 to 4 mm to be made. The implantation of a rigid IOL thus undesirably required enlarging the incision to accommodate the IOL.
In order to take advantage of the small incision size needed to remove the natural lens by the new, so called phacoemulsification procedure, soft deformable or foldable IOLs, initially made from an elastomeric silicone material, were soon developed. When suitably deformed by folding or rolling, these new silicone IOLs could be implanted through the small ocular incision used for the phacoemulsification procedure. After being implanted in the deformed condition, these elastic silicone IOLs would, upon release, return to their original size and condition. Since the time of introduction of the first silicone IOLs other lens materials have been utilized; these include acrylates and the like materials.
As might have been expected, new tools were needed for folding and maintaining a suitable conformation of the IOL prior to and during insertion into the area of the eye previously occupied by the natural lens. Initial efforts were understandably directed to the modification of the types of forceps used to implant rigid PMMA IOLs. However, the folding and maintaining of constant pressure on forceps prior to and during insertion proved to be awkward and difficult in some cases and various inserter or injector devices for implanting deformable IOLs have been developed which do not require the use of forceps for implantation of the IOLs. Most IOL inserter or injector devices still require the preliminary use of forceps for folding or loading the IOLs, or for holding the IOL while it is being deformed and/or for introducing the IOL or its haptics, if present, into the inserter or injector device prior to insertion. Haptics are small wire-like arms of biocompatible material which radiate out from the edge of certain IOLs and serve to hold the optic of the IOL in position inside the eye, a typical IOL comprises two haptics disposed on opposite sides of a substantially circular lens optic.
Representative examples of a few of the above-mentioned types of IOL injector or inserters are disclosed in U.S. Pat. No. 4,681,102 to Bartell; U.S. Pat. No. 4,880,000 to Holmes; U.S. Pat. Nos. 5,066,297, 4,976,716 and 4,862,885 to Cumming; and U.S. Pat. Nos. 5,494,484 and 5,582,614 to Feingold.
Virtually all, if not all, insertion devices have an elongate, slender insertion tube or nozzle at the distal end, designed to be inserted into and through the same, identically sized ocular incision made for phacoemulsification and removal of the natural lens. Proximal to this insertion tube is a region in which the IOL to be implanted is held in a pre-implant, deformed, folded or compressed condition. Proximal as used in this application indicates that portion of the inserter held by or closest to the physician and distal is used to describe that portion closest to or inside the eye.
In many inserter designs the IOL and the inserter sleeve are lubricated with a sterile, lubricous liquid, such as a viscoelastic, to ease resistance to advancing the IOL through the narrow sleeve. Typically, a slender axial shaft is provided in the handle of the insertion device for pushing the folded, rolled or otherwise deformed IOL from the holding region through the nozzle and out the distal end into the eye. The nozzle piece of the inserter is actually placed through the incision in the sclera (the tough white cover of the eye) and typically into the part of the capsular bag that remains after removal of the natural lens.
As the lens is passed through the inserter and prior to being introduced into the eye, the force applied to the inserter can become excessive to the point that the IOL is damaged. For example, the IOL can become adhered to or otherwise difficult to advance through the inserter. Applying too much force to the inserter can result in the IOL becoming damaged. Once released into the eye the optic of the IOL will return to its original shape or configuration whether damaged or not. Removal of a damaged IOL from inside the eye is awkward, time consuming and can result in unwanted surgical complications such as infection or trauma to the cornea of the eye, or the necessity to enlarge the incision in the tissue of the eye. Therefore, it is highly advantageous to avoid damaging the IOL during implantation in the eye.
Typically, the surgeon can sense the resistance to turning or pushing the handle of the inserter while advancing the IOL through the inserter and ascertain if the IOL is advancing properly through the inserter. However, the surgeon is often concerned with many other aspects of the surgery, which include looking into the eye through a microscope, giving instructions, and positioning and holding the inserter in place through the small incision. Since the procedure is performed by observing the placement of the inserter and then lens inside the eye through a microscope, the surgeon is focused on the process as it occurs within the eye, and so potentially is not fully cognizant of the resistance on the inserter handle piece.
Further, with the introduction of new IOL designs and several different types of polymeric materials of IOL construction, there are different resistances experienced when advancing different IOLs through an inserter. For example, an acrylate IOL often requires more force to move through an inserter than does a silicone IOL, and even lenses made of the same or similar materials when made by different processes and/or manufacturers differ in their degree of surface lubricity.
Therefore, it would be highly advantageous to provide a system which effectively limits the amount of force applied to an inserter to an amount which is non-damaging to the IOL.